Beam-Column Connections
Jack Moehle
University of California, Berkeley
with contributions from
Dawn Lehman and Laura Lowes
University of Washington, Seattle
Outline
design of new joints
existing joint details
failure of existing joints in earthquakes
general response characteristics
importance of including joint deformations
stiffness
strength
deformation capacity
axial failure
Special Moment-Resisting Frames
- Design intent Vcol
Mpr
For seismic design,
beam yielding
defines demands
Mpr
lc
w
Mpr
Beam
Vp
Vp
lnb
Vcol
Vp
Mpr
Beam Section
Vcol
Joint demands
Ts1 =
1.25Asfy
C2 = Ts2
Vb2
Vb1
C1 = Ts2
Vcol
Ts2 =
1.25Asfy
(b) internal stress resultants
acting on joint
Vcol
(a) moments, shears, axial
loads acting on joint
Ts1
C2
Vu =Vj = Ts1 + C1 - Vcol
(c) joint shear
Joint geometry
(ACI Committee 352)
ACI 352
a) Interior
A.1
b) Exterior
A.2
d) Roof
Interior B.1
e) Roof
Exterior B.2
c) Corner
A.3
f) Roof
Corner B.3
Joint shear strength
- code-conforming joints -
Vu  Vn  g
 = 0.85
'
c
f bj h
Values of g (ACI 352)
ACI 352
Classification
/type
interior
exterior
corner
cont. column
20
15
12
Roof
15
12
8
Joint Details - Interior
hcol  20db
ACI 352
Joint Details - Corner
 ldh
ACI 352
Code-conforming joints
Older-type beam-column connections
Survey of existing buildings
Mosier
Joint failures
Studies of older-type joints
Lehman
Damage progression
interior connections
80
Yield of Beam
Longitudinal
Reinforcement
60
Spalling of
Concrete Cover
Measurable
residual cracks
Longitudinal
Column Bar
Exposed
Column Shear (K)
40
20
0
20% Reduction
in Envelope
-20
-40
-60
-80
-6
-4
-2
0
Drift %
Lehman
2
4
6
Effect of load history
interior connections
Column Shear (k)
Impulsive loading history
-6
Lehman
Envelope for standard
cyclic history
Column Bar
-4
-2
0
Story Drift
2
4
6
Damage at 5% drift
Standard Loading
Lehman
Impulsive Loading
Contributions to drift
interior connections
120
Column
Percent Contribution
100
Beam
Flexure
Bar Slip
80
60
Joint Shear
40
“Joints shall be modeled
as either stiff or rigid
components.” (FEMA 356)
20
Specimen CD15-14
0
1
Lehman
4
7
10
13
16
19
Cycle Number
22
25
28
31
34
Evaluation of FEMA-356 Model
interior connections
18
Joint Shear Factor
16
14
12
10
FEMA
PEER-14
CD15-14
CD30-14
PADH-14
PEER-22
CD30-22
PADH-22
8
6
4
2
0
0
Lehman
0.005
0.01
0.015
0.02
Joint Shear Strain
0.025
0.03
Joint panel deformations
Joint Deformation
Joint shear stiffness
Joint shear stress (MPa)
interior connections
Lehman
Gc
Gc /5
Gc /8
12
20 f c' , psi
10
8
6
10 f c' , psi
20 f c' , psi
4
2
0
0.000
0.005
0.010
0.015
0.020
Joint shear strain
0.025
0.030
Joint strength
Joint Stress (psi)
effect of beam yielding
1600
Yield
1200
800
400
Yield
0
0
1
2
3
4
5
Drift (%)
• Joint strength closely linked to beam flexural strength
• Plastic deformation capacity higher for lower joint shear
Lehman
6
Joint strength
interior connections - lower/upper bounds
Joint failure without
yielding near
25.5√f’c
0.4
0.3
Failure forced into
beams between
8.5√f’c and 11√f’c
Joint
0.2
Shear
vj/fc’
Failure
0.1
Beam Hinging/
Beam Bar Slip
0
0
10
20
30
L
Lehman
40
50
60
Joint strength
interior connections
Joint Stress (psi)
3500
3000
Joint Failures
2500
2000
1500
1000
10 f c' , psi
500
Beam Failures
0
0
4000
8000
12000
Concrete Strength (psi)
Lehman
16000
Joint Stress (psi)
Joint deformability
1600
plastic drift capacity
1200
vmax
800
0.2vmax
envelope
400
0
0
1
2
3
Drift (%)
4
5
6
Plastic drift capacity
interior connections
v joint
f c'
, psi 30
25
20
15
10
5
0
0
0.01
0.02
0.03
0.04
0.05
0.06
plastic drift angle
Note: the plastic drift angle includes inelastic deformations of the beams
Damage progression
exterior connections
Pantelides, 2002
Joint behavior
exterior connections
v joint
f c'
15
2 Clyde
6 Clyde
4 Clyde
5 Clyde
5 Pantelides
6 Pantelides
6 Hakuto
Priestley longitudinal
Priestley transverse
, psi
10
5
0
0
1
2
3
4
Drift, %
5
6
7
bidirectional
loading
Plastic drift capacity
v joint
f
'
c
, psi 30
Interior
Exterior
25
20
15
10
5
0
0
0.01
0.02
0.03
0.04
0.05
0.06
plastic drift angle
Note: the plastic drift angle includes inelastic deformations of the beams
Exterior joint
hook detail
hook bent into joint
hook bent out of joint
Interior joints with
discontinuous bars
Column
shear,
kips
40
30
20
10
0
0
Beres, 1992
1
2
3
Drift ratio, %
4
5
Unreinforced Joint Strength
FEMA 356 specifies the following:
Vj  g
joint
geometry
f c' bh
• No new data. Probably still valid.
g
4
6
8
10
12
• Assuming bars are anchored in
joint, strength limited by strength of
framing members, with upperbound of g  15. For 15 ≥ g ≥ 4,
joint failure may occur after
inelastic response. For g ≤ 4, joint
unlikely to fail.
• Assuming bars are anchored in
joint, strength limited by strength of
framing members, with upper
bound of g  25. For 25 ≥ g ≥ 8,
joint failure may occur after
inelastic response. For g ≤ 8, joint
unlikely to fail.
Joint failure?
sy
tcr
tcr
t cr  6 f
'
c
1
sy
6 f
'
c
, psi
Joint failure?
Lateral Load
Lateral Deflection, mm
Priestley, 1994
Drift at “tensile failure”
Drift at “lateral failure”
Drift at “axial failure”
Joint test summary
axial failures identified
Tests with axial load failure
0.06
0.20 - 0.22
0.36
0.03 - 0.07
Drift ratio
0.08
0.10 - 0.18
0.1
}
v j  gf c'
Range of g values
Interior
0.04
Exterior, hooks bent in
Exterior, hooks bent out
0.02
Corner
0
0
0.05
0.1
0.15
0.2
Axial load ratio
0.25
0.3
Suggested envelope relation
interior connections with continuous beam bars
0.015
v joint
f
'
c
25
, psi
stiffness based on effective
stiffness to yield
strength = beam strength
but not to exceed 25 f c' , psi
20
15
8
10
5
0
0.04
0.02
Note: the plastic drift angle includes inelastic deformations of the beams
Suggested envelope relation
exterior connections with hooked beam bars
v joint
f c'
, psi
stiffness based on effective
stiffness to yield
25
strength = beam strength
but not to exceed 12 f c' , psi
20
15
0.010
connections with demand less
than 4 f c' have beam-yield
mechanisms and do not follow
this model
10
5
0
0.02
0.01
axial-load stability unknown,
especially under high axial loads
Note: the plastic drift angle includes inelastic deformations of the beams
Joint panel deformations
Joint Deformation
Methods of Repair (MOR)
Method of
Repair
0. Cosmetic
Repair
Activities
Replace and repair finishes
0-2
1. Epoxy Injection Inject cracks with epoxy and
3-5
2. Patching
Patch spalled concrete, epoxy
inject cracks and replace
finishes
6-8
3. Replace
concrete
Remove and replace damaged
concrete, replace finishes
9-11
4. Replace joint
Replace damaged reinforcing
steel, remove and replace
concrete, and replace finishes
12
replace finishes
Pagni
Damage
States
Probability of Requiring a MOR
Interior joint fragility relations
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0 0.0 1.0
Cosmetic repair
Epoxy
MOR
0 injection
MOR
1
Patching
MOR 2
Replace
concrete
MOR
3
Replace
joint
MOR
4
2.0
3.0 4.0
Drift (%)
5.0
6.0
Beam-Column Connections
Jack Moehle
University of California, Berkeley
with contributions from
Dawn Lehman and Laura Lowes
University of Washington, Seattle
References
• Clyde, C., C. Pantelides, and L. Reaveley (2000), “Performance-based evaluation of exterior reinforced
concrete building joints for seismic excitation,” Report No. PEER-2000/05, Pacific Earthquake
Engineering Research Center, University of California, Berkeley, 61 pp.
• Pantelides, C., J. Hansen, J. Nadauld, L Reaveley (2002, “Assessment of reinforced concrete building
exterior joints with substandard details,” Report No. PEER-2002/18, Pacific Earthquake Engineering
Research Center, University of California, Berkeley, 103 pp.
• Park, R. (2002), "A Summary of Results of Simulated Seismic Load Tests on Reinforced Concrete BeamColumn Joints, Beams and Columns with Substandard Reinforcing Details, Journal of Earthquake
Engineering, Vol. 6, No. 2, pp. 147-174.
• Priestley, M., and G. Hart (1994), “Seismic Behavior of “As-Built” and “As-Designed” Corner Joints,”
SEQAD Report to Hart Consultant Group, Report #94-09, 93 pp. plus appendices.
• Walker, S., C. Yeargin, D. Lehman, and J. Stanton (2002), “Influence of Joint Shear Stress Demand and
Displacement History on the Seismic Performance of Beam-Column Joints,” Proceedings, The Third USJapan Workshop on Performance-Based Earthquake Engineering Methodology for Reinforced Concrete
Building Structures, Seattle, USA, 16-18 August 2001, Report No. PEER-2002/02, Pacific Earthquake
Engineering Research Center, University of California, Berkeley, pp. 349-362.
• Hakuto, S., R. Park, and H. Tanaka, “Seismic Load Tests on Interior and Exterior Beam-Column Joints
with Substandard Reinforcing Details,” ACI Structural Journal, Vol. 97, No. 1, January 2000, pp. 11-25.
• Beres, A., R.White, and P. Gergely, “Seismic Behavior of Reinforced Concrete Frame Structures with
Nonductile Details: Part I – Summary of Experimental Findings of Full Scale Beam-Column Joint Tests,”
Report NCEER-92-0024, NCEER, State University of New York at Buffalo, 1992.
• Pessiki, S., C. Conley, P. Gergely, and R. White, “Seismic Behavior of Lightly-Reinforced Concrete
Column and Beam Column Joint Details,” Report NCEER-90-0014, NCEER, State University of New
York at Buffalo, 1990.
• ACI-ASCE Committee 352, Recommendations for Design of Beam-Column Connections in Monolithic
Reinforced Concrete Structures,” American Concrete Institute, Farmington Hills, 2002.
References (continued)
• D. Lehman, University of Washington, personal communication, based on the following resources:
Fragility functions:
•Pagni, C.A. and L.N. Lowes (2006). “Empirical Models for Predicting Earthquake Damage and Repair
Requirements for Older Reinforced Concrete Beam-Column Joints.” Earthquake Spectra. In press.
Joint element:
•Lowes, L.N. and A. Altoontash. “Modeling the Response of Reinforced Concrete Beam-Column Joints.”
Journal of Structural Engineering, ASCE. 129(12) (2003):1686-1697.
•Mitra, N. and L.N. Lowes. “Evaluation, Calibration and Verification of a Reinforced Concrete BeamColumn Joint Model.” Journal of Structural Engineering, ASCE. Submitted July 2005.
•Anderson, M.R. (2003). “Analytical Modeling of Existing Reinforced Concrete Beam-Column Joints”
MSCE thesis, University of Washington, Seattle, 308 p.
Analyses using joint model:
•Theiss, A.G. “Modeling the Response of Older Reinforced Concrete Building Joints.” M.S. Thesis.
Seattle: University of Washington (2005): 209 p.
Experimental Research
•Walker, S.*, Yeargin, C.*, Lehman, D.E., and Stanton, J. Seismic Performance of Non-Ductile
Reinforced Concrete Beam-Column Joints, Structural Journal, American Concrete Institute, accepted
for publication.
•Walker, S.G. (2001). “Seismic Performance of Existing Reinforced Concrete Beam-Column Joints”.
MSCE Thesis, University of Washington, Seattle. 308 p.
•Alire, D.A. (2002). "Seismic Evaluation of Existing Unconfined Reinforced Concrete Beam-Column
Joints", MSCE thesis, University of Washington, Seattle, 250 p.
•Infrastructure Review
•Mosier, G. (2000). “Seismic Assessment of Reinforced Concrete Beam-Column Joints”. MSCE thesis,
University of Washington, Seattle. 218 p.